The goal of this proposal is to understand the role specific molecules play in mediating cellular processes occurring during the development of the nervous system. The underlying assumption is that a set of macromolecules exists whose major function is to determine this course of development. These molecules should be transiently expressed in the nervous system and their presence correlated with the occurrence of the cellular processes they mediate. Such molecules may be absent or distributed in a very different manner in the adult. The cockroach nervous system has been an excellent model for these studies. The relatively small number of neurons, many of which can be individually identified, simplify the anatomical analysis of the cellular events occurring during development. In addition, hybridoma techniques have been used to obtain a library of monoclonal antibodies that transiently bind to various parts of the cockroach nervous system. The developmental stage- specific antigens that these antibodies recognize are excellent candidates for the hypothetical molecular determinants of the development of the nervous system. Experiments are proposed here that will attempt to determine the function of these antigens, molecularly characterize them using recombinant DNA techniques and identify the factors that regulate the expression of the genes coding for them. It is this last part which has the greatest applicability. Some pathological conditions, like cancer, may result from the inappropriate expression of such genes in adult tissue. On the other hand, in some pathological conditions, like spinal and brain damage in response to injury, recuperation is limited by the inability to induce re-expression of these genes in adult tissues where they are usually turned off.